1. Field of Invention
The invention relates to an autostereoscopic screen and, in particular, to an autostereoscopic projection screen.
2. Related Art
The 3D display technology is considered the most research direction after planarization of the displays. The 3D visual effect is to enable a viewer to perceive from a two-dimensional source three-dimensional images as in daily life, i.e. perceiving depths and levels of objects. To display a 3D image, one has to provide two sets of overlapped images in one screen to simulate what two eyes perceive. The two eyes then receive the two sets of images via polarized glasses or gratings. However, the use of polarized glasses brings a lot of inconvenience in practice. To improve the image quality and to achieve the 3D display for naked eyes, many autostereoscopic screens have been invented to directly transmit two sets of images to the left and right eyes separately.
There are many ways to implement a stereoscopic display. A normal stereoscopic projection display uses two projectors to simultaneously provide two sets of images for the left and right eyes, respectively. The images are projected onto a screen with a Fresnel lens that has planar converging power. The action of the Fresnel lens is to deflect tilted incident light from the projector to be perpendicular to the screen. This prevents light from having different incident angles at different positions on the screen; otherwise, it may result in “hot spots” that are bright in the center but dark at the boundary. The two sets of images are then separately guided to the left and right eyes of the viewer to form a 3D image. However, this type of projection equipment does not have a good image quality. Moreover, the size of the structure is large. It is not easy to make a large-size projection screen and may involve a higher cost.
A double lenticular screen in the autostereoscopic projection screen can produce 3D effects too. In this case, both sides of a light diffuser are connected with a lenticular screen. Two projectors simultaneously transmit two sets of images for the left and right eyes, respectively. The image for the left eye passes through the double lenticular screen and enters completely into the left eye. Likewise, the image for the right eye has to be projected only to the right eye of the viewer. To achieve this effect, one had to impose a very stringent requirement on the double lenticular screen. The lenticular screens on both sides have to be completely symmetric. It takes a higher cost and difficult manufacturing process to achieve such a precision.